Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating a semiconductor device includes the steps of: forming a magnetic tunneling junction (MTJ) stack on a substrate; forming a first spin orbit torque (SOT) layer on the MTJ stack; forming a first hard mask on the first SOT layer; and using a second hard mask to pattern the first hard mask, the first SOT layer, and the MTJ stack to form a MTJ.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device, and more particularly to a method for fabricating magnetoresistive random access memory (MRAM).

2. Description of the Prior Art

Magnetoresistance (MR) effect has been known as a kind of effect caused by altering the resistance of a material through variation of outside magnetic field. The physical definition of such effect is defined as a variation in resistance obtained by dividing a difference in resistance under no magnetic interference by the original resistance. Currently, MR effect has been successfully utilized in production of hard disks thereby having important commercial values. Moreover, the characterization of utilizing GMR materials to generate different resistance under different magnetized states could also be used to fabricate MRAM devices, which typically has the advantage of keeping stored data even when the device is not connected to an electrical source.

The aforementioned MR effect has also been used in magnetic field sensor areas including but not limited to for example electronic compass components used in global positioning system (GPS) of cellular phones for providing information regarding moving location to users. Currently, various magnetic field sensor technologies such as anisotropic magnetoresistance (AMR) sensors, GMR sensors, magnetic tunneling junction (MTJ) sensors have been widely developed in the market. Nevertheless, most of these products still pose numerous shortcomings such as high chip area, high cost, high power consumption, limited sensibility, and easily affected by temperature variation and how to come up with an improved device to resolve these issues has become an important task in this field.

SUMMARY OF THE INVENTION

A method for fabricating a semiconductor device includes the steps of: forming a magnetic tunneling junction (MTJ) stack on a substrate; forming a first spin orbit torque (SOT) layer on the MTJ stack; forming a first hard mask on the first SOT layer; and using a second hard mask to pattern the first hard mask, the first SOT layer, and the MTJ stack to form a MTJ.

According to another aspect of the present invention, a semiconductor device includes a magnetic tunneling junction (MTJ) on a substrate, a first spin orbit torque (SOT) layer on the MTJ, second SOT layer on the first SOT layer, and a hard mask between the first SOT layer and the second SOT layer.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 illustrate a method for fabricating a MRAM device according to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-7 , FIGS. 1-7 illustrate a method for fabricating a MRAM device according to an embodiment of the present invention. As shown in FIG. 1 , a substrate 12 made of semiconductor material is first provided, in which the semiconductor material could be selected from the group consisting of silicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC), and gallium arsenide (GaAs), and a MRAM region 14 and a logic region 16 are defined on the substrate 12.

Active devices such as metal-oxide semiconductor (MOS) transistors, passive devices, conductive layers, and interlayer dielectric (ILD) layer 18 could also be formed on top of the substrate 12. More specifically, planar MOS transistors or non-planar (such as FinFETs) MOS transistors could be formed on the substrate 12, in which the MOS transistors could include transistor elements such as gate structures (for example metal gates) and source/drain region, spacer, epitaxial layer, and contact etch stop layer (CESL). The ILD layer 18 could be formed on the substrate 12 to cover the MOS transistors, and a plurality of contact plugs could be formed in the ILD layer 18 to electrically connect to the gate structure and/or source/drain region of MOS transistors. Since the fabrication of planar or non-planar transistors and ILD layer is well known to those skilled in the art, the details of which are not explained herein for the sake of brevity.

Next, metal interconnect structures 20, 22 are sequentially formed on the ILD layer 18 on the MRAM region 14 and the logic region 16 to electrically connect the aforementioned contact plugs, in which the metal interconnect structure 20 includes an inter-metal dielectric (IMD) layer 24 and metal interconnections 26 embedded in the IMD layer 24, and the metal interconnect structure 22 includes a stop layer 28, an IMD layer 30, and metal interconnections 32 embedded in the stop layer 28 and the IMD layer 30.

In this embodiment, each of the metal interconnections 26 from the metal interconnect structure 20 preferably includes a trench conductor and the metal interconnection 32 from the metal interconnect structure 22 on the MRAM region 14 includes a via conductor. Preferably, each of the metal interconnections 26, 32 from the metal interconnect structures 20, 22 could be embedded within the IMD layers 24, 30 and/or stop layer 28 according to a single damascene process or dual damascene process. For instance, each of the metal interconnections 26, 32 could further include a barrier layer 34 and a metal layer 36, in which the barrier layer 34 could be selected from the group consisting of titanium (Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and the metal layer 36 could be selected from the group consisting of tungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Since single damascene process and dual damascene process are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. In this embodiment, the metal layers 36 in the metal interconnections 26 are preferably made of copper, the metal layer 36 in the metal interconnections 32 is made of tungsten, the IMD layers 24, 30 are preferably made of silicon oxide such as tetraethyl orthosilicate (TEOS), and the stop layer 28 is preferably made of nitrogen doped carbide (NDC), silicon nitride, silicon carbon nitride (SiCN), or combination thereof.

Next, a bottom electrode 38, a MTJ stack 40 or stack structure, a top electrode 42, a first spin orbit torque (SOT) layer 44, a hard mask 68, and another mask 46 are formed on the metal interconnect structure 22. In this embodiment, the formation of the MTJ stack 40 could be accomplished by sequentially depositing a pinned layer, a barrier layer, and a free layer on the bottom electrode 38. In this embodiment, the bottom electrode 38 and the top electrode 42 are preferably made of conductive material including but not limited to for example Ta, Pt, Cu, Au, Al, or combination thereof. The pinned layer could be made of ferromagnetic material including but not limited to for example iron, cobalt, nickel, or alloys thereof such as cobalt-iron-boron (CoFeB) or cobalt-iron (CoFe). Alternatively, the pinned layer could also be made of antiferromagnetic (AFM) material including but not limited to for example ferromanganese (FeMn), platinum manganese (PtMn), iridium manganese (IrMn), nickel oxide (NiO), or combination thereof, in which the pinned layer is formed to fix or limit the direction of magnetic moment of adjacent layers. The barrier layer could be made of insulating material including but not limited to for example oxides such as aluminum oxide (AlO_(x)) or magnesium oxide (MgO). The free layer could be made of ferromagnetic material including but not limited to for example iron, cobalt, nickel, or alloys thereof such as cobalt-iron-boron (CoFeB), in which the magnetized direction of the free layer could be altered freely depending on the influence of outside magnetic field. Preferably, the first SOT layer 44 is serving as a channel for the MRAM device as the first SOT layer 44 could include metals such as tantalum (Ta), tungsten (W), platinum (Pt), or hafnium (Hf) and/or topological insulator such as bismuth selenide (Bi_(x)Se_(1-x)). The hard mask 68 preferably includes conductive material or metal such as ruthenium (Ru) and the hard mask 46 could include conductive or dielectric material including but not limited to for example TiN.

Next, as shown in FIG. 2 , an etching process or more specifically a photo-etching process to pattern the hard mask 46 for exposing the surface of the hard mask 68 underneath. Specifically, the photo-etching process could be accomplished by first forming a patterned mask (not shown) such as patterned resist on the hard mask 46, and then an etching process is conducted by using the patterned mask to remove part of the hard mask 46 for forming a patterned hard mask 46 and exposing the surface of the hard mask 68. Preferably, the etching process conducted at this stage includes a reactive ion etching (ME) process and the hard mask 68 preferably serves as an etching stop layer so that when the ME process is conducted to remove part of the hard mask 46 the etchant used could stop on the surface of the hard mask 68 without damaging or affecting the magnetic materials in the MTJ stack 40 underneath.

Next, as shown in FIG. 3 , one or more etching process could be conducted to by using the patterned mask 46 as mask to remove part of the first SOT layer 44, part of the top electrode 42, part of the MTJ stack 40, part of the bottom electrode 38, and part of the IMD layer 30 to form a MTJ 48 on the MRAM region 14, and the patterned mask 46 is removed thereafter. It should be noted that an ion beam etching (IBE) process instead of a ME process is conducted at this stage to remove the top electrode 42, MTJ stack 40, bottom electrode 38, and the IMD layer 30 in this embodiment for forming the MTJ 48. Due to the characteristics of the IBE process, the top surface of the remaining IMD layer 30 is slightly lower than the top surface of the metal interconnections 32 after the IBE process and the top surface of the IMD layer 30 also reveals a curve or an arc. It should also be noted that as the IBE process is conducted to remove part of the IMD layer 30, part of the metal interconnection 32 could be removed at the same time to form inclined sidewalls on the surface of the metal interconnection 32 immediately adjacent to the MTJ 48. Moreover, all of the remaining hard mask 46 is removed at the same time as the etching process is conducted to remove the aforementioned material layers so that only the hard mask 68 is disposed on the first SOT layer 44. Preferably, the width of the hard mask 68 is equal to the widths of the first SOT layer 44 and the MTJ 48 underneath after the etching process.

Next, a cap layer 50 is formed on the MTJ 48 while covering the surface of the IMD layer 30 on the MRAM region 14 and the logic region 16. In this embodiment, the cap layer 50 preferably includes silicon nitride, but could also include other dielectric material including but not limited to for example silicon oxide, silicon oxynitride (SiON), or silicon carbon nitride (SiCN).

Next, as shown in FIG. 4 , an etching process is conducted without using any patterned mask such as patterned resist to remove part of the cap layer 50 for forming a spacer 66 around or adjacent to sidewalls of the MTJ 48, the first SOT layer 44, and the hard mask 68, in which the spacer 66 preferably includes a L-shape in a cross-section view. Next, a deposition process such as an atomic layer deposition (ALD) process is conducted to form an IMD layer 52 on the hard mask 68, the spacer 66, and the IMD layer 30, and then a planarizing process such as a chemical mechanical polishing (CMP) or etching back process is conducted to remove part of the IMD layer 52 so that the top surface of the remaining IMD layer 52 is even with the top surface of the hard mask 68.

Next, as shown in FIG. 5 , a second SOT layer 54 is formed on the surface of the hard mask 68 and the IMD layer 52. Next, a pattern transfer or photo-etching process is conducted by using a patterned mask (not shown) as mask to remove part of the second SOT layer 54 on the IMD layer 52 as the remaining second SOT layer 54 is still disposed on the IMD layer 52 adjacent to two sides of spacer 66. In this embodiment, the first SOT layer 44 and the second SOT layer 54 are preferably made of same material, in which the second SOT layer 54 also serves as the channel for MRAM device and the second SOT layer 54 could include metals such as tantalum (Ta), tungsten (W), platinum (Pt), or hafnium (Hf) and/or topological insulator such as bismuth selenide (Bi_(x)Se_(1-x)).

Next, as shown in FIG. 6 , another IMD layer 56 is formed on the second SOT layer 54 and the IMD layer 52, in which the IMD layer 56 is preferably formed conformally on the second SOT layer 54. In this embodiment, each of the IMD layer 52 and IMD layer 56 preferably includes an ultra low-k (ULK) dielectric layer including but not limited to for example porous material or silicon oxycarbide (SiOC) or carbon doped silicon oxide (SiOCH). Next, a planarizing process such as chemical mechanical polishing (CMP) process or etching back process is conducted to remove part of the IMD layer 56 while the top surface of the remaining IMD layer 56 is still higher than the top surface of the second SOT layer 54.

Next, a pattern transfer process is conducted by using a patterned mask (not shown) to remove part of the IMD layer 56, part of the IMD layer 52, part of the IMD layer 30, and part of the stop layer 28 on the MRAM region 14 and logic region 16 to form contact holes (not shown) exposing the metal interconnections 26 underneath and conductive materials are deposited into the contact hole afterwards. For instance, a barrier layer selected from the group consisting of titanium (Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and metal layer selected from the group consisting of tungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP) could be deposited into the contact holes, and a planarizing process such as CMP could be conducted to remove part of the conductive materials including the aforementioned barrier layer and metal layer to form metal interconnections 58 in the contact holes electrically connecting the metal interconnections 26.

Next, as shown in FIG. 7 , a stop layer 60 is formed on the MRAM region 14 and logic region 16 to cover the IMD layer 56 and metal interconnections 58, an IMD layer 62 is formed on the stop layer 60, and one or more photo-etching process is conducted to remove part of the IMD layer 62, part of the stop layer 60, and part of the IMD layer 56 on the MRAM region 14 and logic region 16 to form contact holes (not shown). Next, conductive materials are deposited into each of the contact holes and a planarizing process such as CMP is conducted to form metal interconnections 64 connecting the MTJ 48 and metal interconnections 58 underneath, in which the metal interconnections 64 on the MRAM region 14 directly contacts the second SOT layer 54 underneath while the metal interconnections 64 on the logic region 16 directly contacts the metal interconnections 58 on the lower level.

In this embodiment, the stop layers 60 and 28 could be made of same or different materials, in which the two layers 60, 28 could all include nitrogen doped carbide (NDC), silicon nitride, silicon carbon nitride (SiCN), or combination thereof. Similar to the metal interconnections formed previously, each of the metal interconnections 64 could be formed in the IMD layer 62 through a single damascene or dual damascene process. For instance, each of the metal interconnections 64 could further include a barrier layer and a metal layer, in which the barrier layer could be selected from the group consisting of titanium (Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and the metal layer could be selected from the group consisting of tungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Since single damascene process and dual damascene process are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. This completes the fabrication of a semiconductor device according to an embodiment of the present invention.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A method for fabricating a semiconductor device, comprising: forming a magnetic tunneling junction (MTJ) stack on a substrate; forming a first spin orbit torque (SOT) layer on the MTJ stack; forming a first hard mask on the first SOT layer; and using a second hard mask to pattern the first hard mask, the first SOT layer, and the MTJ stack to form a MTJ.
 2. The method of claim 1, wherein the substrate comprises a magnetic random access memory (MRAM) region and a logic region, the method comprising: forming a first inter-metal dielectric (IMD) layer on the substrate; forming a first metal interconnection in the first IMD layer on the MRAM region; forming the MTJ stack on the first IMD layer and the first metal interconnection; forming the first SOT layer on the MTJ stack; forming the first hard mask on first SOT layer; forming a second hard mask on the first hard mask; performing a first etching process to pattern the second hard mask for exposing the first hard mask; and performing a second etching process to pattern the first hard mask, the first SOT layer, and the MTJ stack to form the MTJ on the first metal interconnection.
 3. The method of claim 2, wherein the first etching process comprises a reactive ion etching (ME) process.
 4. The method of claim 2, wherein the second etching process comprises an ion beam etching (IBE) process.
 5. The method of claim 2, further comprising performing the second etching process to remove the second hard mask completely.
 6. The method of claim 2, further comprising: forming a cap layer on the first hard mask and the first IMD layer; removing the cap layer to form a spacer around the MTJ; forming a second IMD layer around the spacer; forming a second SOT layer on the first hard mask and the second IMD layer; patterning the second SOT layer; forming a third IMD layer on the second SOT layer; and forming a second metal interconnection on the logic region.
 7. The method of claim 6, wherein top surfaces of the second IMD layer and the first hard mask are coplanar.
 8. The method of claim 6, wherein top surfaces of the second IMD layer and the spacer are coplanar.
 9. The method of claim 6, further comprising: forming a stop layer on the third IMD layer; forming a fourth IMD layer on the stop layer; forming a third metal interconnection on the MUM region to connect to the second SOT layer; and forming a fourth metal interconnection on the logic region to connect to the second metal interconnection.
 10. The method of claim 1, wherein the first hard mask comprises ruthenium (Ru).
 11. A semiconductor device, comprising: a magnetic tunneling junction (MTJ) on a substrate; a first spin orbit torque (SOT) layer on the MTJ; a second SOT layer on the first SOT layer; and a hard mask between the first SOT layer and the second SOT layer.
 12. The semiconductor device of claim 11, wherein the substrate comprises a magnetic random access memory (MRAM) region and a logic region, the semiconductor device comprising: a first inter-metal dielectric (IMD) layer on the substrate; a first metal interconnection in the first IMD layer on the MRAM region; the MTJ on the first metal interconnection; a second IMD layer around the MTJ; and a second metal interconnection in the second IMD layer on the logic region.
 13. The semiconductor device of claim 12, further comprising a spacer adjacent to the MTJ, the first SOT layer, and the hard mask.
 14. The semiconductor device of claim 13, wherein a top surface of the spacer is even with a top surface of the hard mask.
 15. The semiconductor device of claim 12, further comprising: a stop layer on the second IMD layer; a third IMD layer on the stop layer; a third metal interconnection on the MRAM region to connect to the second SOT layer; and a fourth metal interconnection on the logic region to connect to the second metal interconnection.
 16. The semiconductor device of claim 11, wherein a width of the hard mask is equal to a width of the first SOT layer.
 17. The semiconductor device of claim 11, wherein the hard mask comprises ruthenium (Ru). 